#include <stdio.h>
#include <stdlib.h>
#include <netdb.h>   /* for getservbyname */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <sys/time.h>

int main(int argc, char **argv)
{
	struct sockaddr_in address;
	char buffer[INET_ADDRSTRLEN];   /* for inet_pton */
	struct hostent *entry;          /* for gethostbyname, gethostbyaddr */
	int s;                          /* file descriptor */

	bzero((char *)&address, sizeof address);
	address.sin_family = AF_INET;

	if (argc == 2) {   /* one command line argument */
		const struct servent *const p = getservbyname("telnet", "tcp");
		if (p == NULL) {
			fprintf(stderr, "%s: couldn't find telnet port number\n",
				argv[0]);
			return 1;
		}
		address.sin_port = p->s_port;
	}

	else if (argc == 3) {   /* two command line arguments */
		if (sscanf(argv[2], "%hd", &address.sin_port) != 1) {
			fprintf(stderr, "%s: %s is not a legal port number\n",
				argv[0], argv[2]);
			return 2;
		}
		address.sin_port = htons(address.sin_port);
	}

	else {
		fprintf(stderr, "%s: usage hostname [port]\n", argv[0]);
		return 3;
	}

	entry = gethostbyname(argv[1]);
	if (entry == NULL) {
		fprintf(stderr, "%s: gethostbyname, h_errno == %d\n",
			argv[0], h_errno);
		return 4;
	}
	address.sin_addr.s_addr = *(in_addr_t *)entry->h_addr_list[0];

	s = socket(AF_INET, SOCK_STREAM, 0);
	if (s < 0) {
		perror(argv[0]);
		return 5;
	}

	if (inet_ntop(AF_INET, &address.sin_addr, buffer, sizeof buffer) == NULL) {
		perror(argv[0]);
		return 6;
	}
	printf("Trying %s...\n", buffer);

	if (connect(s, (struct sockaddr *)&address, sizeof address) != 0) {
		perror(argv[0]);
		return 7;
	}

	entry = gethostbyaddr((char *)&address.sin_addr, sizeof address.sin_addr,
		AF_INET);
	if (entry == NULL) {
		fprintf(stderr, "%s: gethostbyaddr, h_errno == %d\n",
			argv[0], h_errno);
		return 8;
	}
	printf("Connected to %s.\n", entry->h_name);

	for (;;) {
		fd_set readset;              /* set of file descriptors */
		struct timeval t = {0, 0};   /* seconds, microseconds */
		char c;
		int n;

		FD_ZERO(&readset);
		FD_SET(s, &readset);
		FD_SET(fileno(stdin), &readset);

		if (select(s + 1, &readset, NULL, NULL, &t) < 0) {
			perror(argv[0]);
			return 9;
		}

		if (FD_ISSET(s, &readset)) {
			/* We can call the following read without getting stuck. */
			n = read(s, &c, 1);
			if (n < 0) {
				perror(argv[0]);
				return 10;
			}
			if (n == 0) {   /* Received end of file from the server */
				printf("Connection closed by foreign host.\n");
				break;
			}
			if (write(fileno(stdout), &c, 1) != 1) {
				perror(argv[0]);
				return 11;
			}
		}

		if (FD_ISSET(fileno(stdin), &readset)) {
			/* We can call the following read without getting stuck. */
			n = read(fileno(stdin), &c, 1);
			if (n < 0) {
				perror(argv[0]);
				return 12;
			}
			if (n == 0) {   /* Received end of file from the stdin. */
				printf("Connection closed.\n");
				break;
			}
			if (write(s, &c, 1) != 1) {
				perror(argv[0]);
				return 13;
			}
		}
	}

	if (shutdown(s, SHUT_RDWR) != 0) {
		perror(argv[0]);
		return 11;
	}

	return EXIT_SUCCESS;
}